Whole human blood includes blood cells such as red blood cells, white blood cells and platelets and these cells are suspended in plasma, an aqueous solution of proteins and other chemicals. Blood transfusions used to be made using whole blood. Recently, however, blood transfusions are widely given by transfusing only those blood components required by a particular patient instead of using a transfusion of whole blood. Transfusing only those blood components necessary saves the available supply of blood, and in many cases, is convenient for the patient.
Centrifugation has been widely accepted as a technique for separating blood components such as plasma and platelets from whole blood, wherein blood components are separated depending upon their specific gravities. Disposable centrifuge rotors or bowls have been developed for separating blood components by such centrifugation and for washing blood cell components collected from a surgical site.
Typical examples include a centrifuge bowl of the type disclosed in U.S. Pat. No. 4,300,717 ("Latham" bowl) and a centrifuge bowl of the type disclosed in U.S. Pat. No. 4,086,924 ("Grenade" bowl). The bowl in each case comprises a rotor portion in which blood components are separated and a stator portion having an inlet port and an outlet port, and a rotary seal combines these portions together. Anticoagulated whole blood and/or wash solution is introduced to the interior of the rotor portion through the inlet port. The rotor portion rotates at a fixed or variable speed and blood components within the rotor portion are separated by centrifugation in accordance with their specific gravities. With blood continuously entering the bowl through the inlet port, the separated various blood components are progressively displaced inwardly from the radially outward portion of the bowl and successively reach a skirt portion which opens radially outwardly and communicates with the outlet port. Blood components exiting through the outlet port are retained and stored, while components remaining in the bowl after collection is complete are then returned to the patient or donor through the outlet port, or deposited in an appropriate container for preservation. The rotor portion comprises a generally frustoconical or cylindrical bowl body and a generally cylindrical core is coaxially disposed therein as the stator portion. Separation by centrifugation is achieved in the space between the core and the bowl body, i.e., a separation chamber. The rotary seal is constructed as a rotary seal assembly including the inlet port and the outlet port and a collection chamber, which is a space for guiding the separated blood components to the outlet port, is formed between the seal and the top of the core. Openings are provided about the core periphery for communication between the separation chamber and the collection chamber. A central opening is formed in the core and a stem for guiding fluid from the inlet port to the lower portion of the bowl is inserted through the central opening.
In addition to the bowls of the above constructions, U.S. Pat. Nos. 4,983,158 and 4,943,273 disclose another types of bowls which are herein referred to as "BM bowl". These bowls include an integral bowl body formed by blow molding and cores of various shapes can be coaxially inserted into the bowl through an aperture formed in one axial end of the bowl body. The bowl of U.S. Pat. No. 4,943,273 features a diverter member, which can be fitted into the bowl by insertion, is provided below the core so that the bowl would be suitable for washing blood cell components collected from a surgical site.
Further, U.S. Pat. No. 5,100,372 discloses an improved core adapted for insertion into a BM bowl, wherein it is taught to provide the core with small size openings for communication between the separation chamber and the collection chamber, so that any blood components remaining on the upper portion of the core can be effectively removed by "splash back".
Moreover, International Publication WO94/08721 pamphlet (PCT/US93/09276) discloses a core for a Grenade bowl for use in blood cell separation or washing, in which the core is provided with a plurality of radially outwardly extending projections for minimizing formation of Coriolis waves which would otherwise cause undesirable turbulence in the separation chamber. Furthermore, a bowl of the BM type for washing or concentrating red blood cells and having only the upper core portion without a body that coaxially extends with the bowl body, is disclosed in International Publication WO89/01792 pamphlet (PCT/US88/02963). Furthermore, U.S. Pat. No. 5,045,048 discloses another type of Latham type bowl. In FIG. 1 of this U.S. Patent, the radially outward periphery of skirt portions 24a and 25a communicating the outlet port is shown closely adjacent to the inner wall of the bowl body. However, no detailed explanation is given.